In the last twenty years or so, there has been a growing emphasis in the forestry business on developing logging systems which depend upon air lifting of the logs out of the cutting area. These logging systems depend primarily on helicopters, designed to lift heavy loads, and also upon balloons and airships. Such aerial systems increase the efficiency of the lumbering operations through larger lift capacities, improved access to remote timber which perhaps could be reached in no other way, and reduced construction costs for roads for trucks. The expense of trucking is also substantially reduced. The "bottom-line" result is lower primary transportation cost per unit volume of timber. Another very important advantage is that the overall impact on the envionrment is greatly reduced.
However, such aerial systems, for maximum efficiency, require accurate estimates of the trees to be harvested. These estimates include sizes of the trees, weights of the logs, and total weight of the stand of timber to be harvested. If these estimates are wrong to a significant extent, various problems result. It may be found that the helicopter cannot lift a particular log at all. On the other hand, if the logs are cut too small, then the helicopters will be underloaded, and this will result in extra flying time, which reduces efficiency and increases costs. Further, depending upon the total weight of harvested trees to be removed, and their distribution as to sizes, both lengths and diameters, the managers can select the particular type of equipment and schedule the number of manhours to closely match the requirements of the work, thus eliminating any wasted time, and using the most efficient logging and airlifting capabilities for the particular project requirements.
Although the forest industry has recognized the above considerations since the early 1960's, when heavy lift aerial logging came into use, methods and apparatus to generate accurate estimates of green log weights has received little attention, prior to the present invention.
Generally, in order to provide an accurate estimate for a single tree, the two important variables are the volume and green density of the entire bole. Green density is considered as the dry density of the wood plus the moisture plus the weight of the bark. Put another way, green weight is simply the weight of the freshly cut bole.